The main pro-Russian rebel leader in eastern Ukraine says his troops are on the offensive and he does not want truce talks with Kiev.
Alexander Zakharchenko said his forces would push the front line back to the borders of Donetsk region. They are in control of the city of Donetsk.
Russian President Vladimir Putin accused Ukrainian government forces of “criminal” shelling of civilian areas.
Kiev “ordered the start of major combat operations” along the front, he said.
Earlier, Mr Zakharchenko said the rebels “will not make any attempts at ceasefire talks any more”.
Ukraine, Russia, France and Germany have issued a call to end fighting.
On Thursday, Ukrainian government troops withdrew from Donetsk airport’s main terminal, a scene of bitter fighting in recent weeks.
The government said the military still retained control of parts of the airport, but six soldiers had died and 16 had been wounded.
The government and its Western allies say Russian regular troops are fighting alongside the separatists, using Russian heavy artillery and tanks. Moscow insists that only Russian “volunteers” have joined the rebels.
Mr Zakharchenko said “we’ll attack right up to the borders of Donetsk region, but if I see a threat from other directions we’ll neutralise it”.
“Kiev doesn’t understand now that we can attack in three directions simultaneously,” Russian media quoted him as saying.
More than 5,000 people have been killed in fighting since the rebels seized a large swathe of Donetsk and Luhansk regions last April, UN officials say. More than a million people have been displaced.